Gene silencing using small interfering RNAs (siRNAs) has become a powerful method for studying gene function. The use of siRNAs often accelerates applications such as target validation, gene discovery, tissue engineering and gene therapeutic approaches. siRNAs are often used by researchers to reduce the expression of specific genes in mammalian cells. Researchers may design siRNAs or purchase validated siRNAs for their target of interest and transfect them into culture cells. Human primary cells are often desired for such experiments because they are more similar to their in vivo counterparts than are immortalized cells. However, common chemical-based transfection methods that work well for cell lines often fail to transfect primary cells.
One technique that has been used with considerable success to deliver siRNA to cells (including primary cells) is electroporation. Electroporation involves applying an electric field pulse to cells to induce the formation of microscopic pores (electropores) in the cell membrane allowing molecules, ions, and water to traverse the destabilized cell membrane. The transfer of nucleic acids to cells by electroporation is an effective method for achieving high efficiency transfections in vitro and in vivo. Under specific pulse conditions, the electropores reseal and the “electroporated” cells recover and continue to grow.
Successfully delivering functional siRNA to cells typically requires that several optimum electroporation conditions be determined. To determine optimal electroporation conditions, a comprehensive set of data is usually generated from a collection of different transfection conditions including: testing various electrical wave-forms, types of electroporation buffers, different temperatures, and cell densities. Careful examination of these parameters for a new cell type typically requires lengthy processing times using standard cuvette-based electroporation methods.
In some electroporation environments successful delivery and cell viability depend on multiple electrical parameters such as: field strength (primarily voltage in relation to gap width), pulse length, and number of pulses. Determining the optimum electroporation conditions for delivering siRNA is typically a lengthy and costly process. Additional experimentation may then be carried out to test multiple different siRNAs in various amounts to modulate the target gene (or genes) to a desired level of expression.
A significant drawback to electroporation is the format in which it is conducted. Commercially available electroporation instruments use sample cuvettes and require significant amounts of preparation. This limits the number and types of experiments that can be performed, incurs the expense of using a specialized cuvette to deliver the desired pulse to the sample, and requires significant time and effort to deposit samples within the cuvettes, deposit the cuvettes in an appropriate apparatus, and to remove the electroporated sample from the cuvette.